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Post by donkeychomp on Sept 5, 2019 23:48:14 GMT 1
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Post by bare on Sept 9, 2019 22:26:21 GMT 1
In theory anything that smooths airflow is better than open carb mouths alone .
Try em on a Dyno or track and see ?
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Post by Deleted on Sept 10, 2019 11:01:39 GMT 1
Good theory, except a few years ago Honda actually had the inner surface of their inlet trumpets made like the surface of a golf ball
The idea was to get the air to become turbulent to better mix the fuel with it therefore giving a better burn and thus more power
Turbulent flow, as in being able to measure the volume of air before the fuel mixing, is hard to measure, thus the air flow going through an air box ideally needs to be laminar because it is a smooth flow and more easily measured and modelled by the modern mass airflow sensor
That way the correct amount of fuel can be added to that volume of air measured more or less every millisecond
It doesn't matter that much with our bikes as there is no MAF sensor, however one would expect that you would want some turbulence somewhere in the carby to mix oil, fuel and air, most likely on the outlet side
That said the rotation of the crank and the up down motion of the conrods in the crank case help this situation somewhat and help in that mixing process by bashing the mixture around at fairly high revs
Being a 2 stoke not all the air/fuel/oil mixture get burnt in any case a sizeable proportion of it goes straight out the exhaust ports into the exhaust
There are a few very clever people on here and around the world that do mess with this and each i guess will have their own theory
This is just mine
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Post by shaunthe2nd on Sept 10, 2019 15:05:47 GMT 1
I inherited some with a job lot that I won't use. You can have them for the cost of postage if you want to try some. No jubilee clips with mine. Slide over the air side of the carb, approx 42ishmm diameter.
PM me your number and I will Whattsapp you some pics if you want.
Shaun
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Post by bare on Sept 10, 2019 17:16:26 GMT 1
Mebe :-) preventing boundary layer airflows from 'sticking' to inlet walls, thereby reducing effective inlet diameter..
(the purpose in dimpled surfaces).. is an Entirely different, additional advancement on a tapered duct with a radiused edge inlet.
A raw Carb mouth alone is not good aero design by any yardstick.
There is reason why aircraft engine inlets (yes some war machines differ, but that's a serious digression) are radiused and smoothed all the way into the compressor blades.
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Post by Tobyjugs on Sept 10, 2019 22:54:26 GMT 1
Not sure if this is good for this thread but i would like to share my experience with Howard and Bare. I modified the complete inlet manifold from my standard carbs to the end of my reeds. The billet manifold i used was sleeved to reduce the inlet diameter. The side where the carbs were fitted was 26 mm just like the carbs, The other side where the reeds blocks sit was 28 mm, the idea was to create a smooth flow without too much turbulence. No mixture of different diameter parts. I was warned by Tony Doukas not to make the surface too smooth as the fuel will stick to it causing big drops once enough collects and becomes airborne again. The front of the reeds were stuffed to 28 mm as well. The idea behind the 2 mm expanding taper was to create the same action that happens at the front of an expansion pipe. The reed cage was aerodynamically modified so that no turbulence was created when the mixture hit the tip at the end of the reed cage, This was me trying to pinch or use the ideas from Ed Erlanbach's web site and studying the design of the V-Force reeds. The end result was an extra 5 hp but the mixture was too lean as the above ideas rendered the standard carbs useless. They could not flow enough fuel. I have now fitted 28 mm PWK's which makes all the above mods useless as i now have to mod the inlet manifold from 28 mm to 30 mm  |
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Post by donkeychomp on Sept 10, 2019 22:55:41 GMT 1
Shaun, PM sent.
Lads thanks for all the advice. As always, invaluable!
Alex
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Post by Deleted on Sept 11, 2019 1:23:14 GMT 1
I think we all need to study hydrodynamics and mass flow
Really interesting insight by bare and tj, some really good info ther
You can see what i mean by different theories behind air flow and fuel mix in a carburettor
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Post by veg on Sept 13, 2019 16:09:59 GMT 1
Brother used to build race car engines admittedly four strokes before four stroke drag engines. He was also in Indy car racing in the states he used to say that the ideal behind flowing is a smooth passage but never mirrored polishing precisely for the reasons above. You need the surface to be able to disturb the flow sufficiently to help mix but not enough to interrupt it. Then he used to bang on about formulae and flow dynamics and characteristics that was usually the time I had fallen asleep.
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Post by madmick on Sept 13, 2019 17:02:30 GMT 1
That’s dead on that. They stopped mirror finishing years back because they found out the fuel/air wasn’t mixing properly.
M.M.
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Post by donkeychomp on Sept 13, 2019 22:48:22 GMT 1
They turned up today and fit perfectly. Nice one Shaun!
Alex
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